Cogent IPv6

Owen DeLong owen at
Thu Jun 9 08:32:58 UTC 2011

On Jun 8, 2011, at 7:24 PM, William Herrin wrote:

> On Wed, Jun 8, 2011 at 9:58 PM, Kelly Setzer <Kelly.Setzer at> wrote:
>> IPv6 newbie alert!
>> I thought the maximum prefix length for IPv6 was 64 bits,
>> so the comment about a v6 /112 for peering vexed me.  I
>> have Googled so much that Larry Page called me and
>> asked me to stop.
>> Can someone please point me to a resource that explains
>> how IPv6 subnets larger than 64 bits function and how
>> they would typically be used?
> Hi Kelly,
> IPv6 netmasks work exactly like IPv4 netmasks. You can even route
> /128's if you want. Two major caveats:
> 1. SLAAC (stateless autoconfiguration, the more or less replacement
> for DHCP) only works if the subnet on your LAN is exactly /64. So
> unless you're manually configuring the IPv6 address on every machine
> on your subnet, you're using a /64.
You can actually use DHCPv6 to assign addresses to hosts dynamically
on longer than /64 networks.

However, you may have to go to some effort to add DHCPv6 support to
those hosts first.


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